A. Field of Invention
The present invention relates to the art of Zero Turn Radius drive systems utilizing a steering wheel, and more specifically to a Zero Turn Radius drive system using one pump in conjunction with two motors.
B. Description of the Related Art
It is known in the art to provide vehicles with drive systems that provide for Zero Turn Radius steering. Typically, Zero Turn Radius vehicles, or ZTR vehicles, provide dual steering levers that are independently operated for use in steering and propelling the vehicle. Each of the dual steering levers are connected to a respective drive device, such as a hydrostatic drive, that are, in turn, connected to individual ground engaging wheels for use in propelling and steering the vehicle.
Such ZTR vehicles provide for greater mobility of the vehicle, in that the ZTR vehicle can make tighter returns. However, the operator is required to learn how to steer a ZTR vehicle with the dual lever steering system, which is inherently different from the usual steering wheel adapted for use on most driving vehicles and cumbersome to inexperienced operators.
Some devices incorporate a steering wheel onto a ZTR vehicle. One such device is disclosed in U.S. Pat. No. Re 34,057, which includes a driving and steering mechanism for a vehicle having a pair of driving wheels. The patent further discloses that the driving and steering mechanism includes a pair of floating links pivotally connected at one end to a respective transmission control arm. The floating links are further disclosed to operate so as to integrate outputs from a steering wheel and an accelerator foot pedal.
One aspect of the aforementioned device is that the mechanism does not allow for proper steering, when the vehicle is being propelled in the reverse direction; as its does when the vehicle is being propelled in the forward direction. In the instance, where the accelerator pedal is engaged to drive the vehicle in a forward direction and where the steering wheel is turned so as to provide a right turn, depressing the accelerator pedal causes the vehicle to make a right-hand forward turn. With the steering wheel still turned to make a right hand turn and where the accelerator pedal is now engaged to drive the vehicle in the reverse direction, the device of Pat. No. Re 34,057 causes the steering mechanism of the vehicle to make a left-hand rearward turn, instead of a right-hand rearward turn, usually associated with vehicles incorporating a steering wheel.
The present invention obviates the aforementioned problem, while providing a cost effective and efficient hydrostatic drive system. Still, other objects and advantages of the invention will appear from the following detailed description of the preferred embodiment of the invention with reference being made to the accompanying drawings.
It is an object of the present invention to provide a steering mechanism that utilizes hydrostatic drives to provide for the proper steering of a ZTR vehicle in both the reverse in forward directions.
It is another object of the present invention to provide a drive system that utilizes a single hydraulic pump in conjunction with two hydraulic motors to propel and steer a ZTR vehicle.
Is still another object of the present invention to provide a drive system that utilizes a double acting variable displacement hydraulic pump, in conjunction with dual double acting variable displacement hydraulic motors.
It is yet another object of the present invention to provide a drive system that incorporates a steering wheel onto a ZTR vehicle.
It is still yet another object of the present invention to provide a drive system that incorporates a steering wheel, operably connected to dual hydraulic motors, for use in steering a ZTR vehicle.
It is yet another object of the present invention to provide a lawnmower having ZTR capabilities that incorporate a steering wheel in conjunction with a single pump and two hydraulic motors.
It is yet another object of the present invention to provide an accelerator peddle that is connected to a single variable displacement hydraulic pump that operates to selectively adjust the speed and direction in which the vehicle is propelled.
It is another object of the present invention to provide a ZTR vehicle that incorporates a steering wheel and an accelerator peddle into a hydrostatic drive system that provides for proper steering in the forward and reversed directions.
It is still yet another object of the present invention to provide a ZTR vehicle having steering input that functions independent from that of the accelerating input of the vehicle.
There is provided in the present invention a drive system that incorporates a single double acting variable displacement hydraulic pump that is communicated by way of a fluid power hydraulic circuit, in parallel, to two double acting variable displacement hydraulic motors. Each of the two variable displacement hydraulic motors are respectively connected to one of two ground engaging wheels, so as to transfer rotational power from the motor to the wheel for use in steering and propelling the vehicle. The hydraulic pump includes a pintle shaft that is mechanically connected to an accelerator pedal. The accelerator pedal is selectively operable to be adjusted in first and second directions about a fixed pivot point. When the accelerator pedal is adjusted in the first direction, mechanical linkage from the pedal to the pintle shaft engages the hydraulic pump to provide fluid power in the first direction. Likewise, when the accelerator pedal adjusted in the second direction, fluid power from the hydraulic pump flows in a reverse direction. A steering wheel is included that is mechanically connected to the hydraulic motors. First and second steering links are respectively connected, one to each of the pintle shafts on the hydraulic motors. When the steering wheel is selectively adjusted in a first direction, the pintle shaft on the first hydraulic motor is adjusted toward a first direction, wherein the power output to the first drive wheel is increased with respect to a forward direction of travel. At the same time, the pintle shaft on the second hydraulic motor is adjusted toward a second direction, wherein the power output of the drive wheel is decreased with respect to a forward direction of travel. In this manner, when the steering wheel is adjusted in a first direction, depressing the accelerator pedal causes the vehicle to make a forward turn in the first direction. Likewise, with the steering wheel still turned in the first direction and when the accelerator peddle is engaged in a second direction so as to drive the vehicle in reverse, the ZTR vehicle makes a rearward turn in the first direction.